VoLTE support progress

Also just to add, but the T-Mobile news about dropping support was leaked to the press early - during a pandemic where they’re looking to still turn a profit is a bad time to not be able to control the narrative.

Id’d not be surprised if this stops being a goal for them for a little while longer, while they continue to refarm existing spectrum without risking any sort of official action until it can be seen as more politically correct to do so.

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The fact remains, though, that if you’re on T-Mobile or a T-Mobile MVNO, and the 3G signal where you live, work, move around, or travel is either very weak or non-existent, and you’re using a non-VoLTE phone, then your incoming and outgoing calls will probably not connect. Your phone will likely not even ring (in or out) as it drops to 3G and looks for the signal. That’s what was happening with my Android on T-Mobile MVNOs…and I didn’t even realize it for weeks.

Calls didn’t go to my voicemail, either.


Wouldn’t all the VoLTE fooforah be moot if AweSIM included a libre service that worked like Google Voice? :kissing_closed_eyes:

Speaking of that, and somewhat related, I tried to install Linphone on the L5 a while back, but it didn’t work out so well. Maybe with Byzantium…

Look at Mycroft AI

For what it’s worth, I have been testing out VoLTE over T-Mobile networks by enabling the VoLTE mode on the Librem 5 modem (which is disabled by default right now). Once enabled, I can successfully receive calls over 4G.

Unfortunately when I attempt to place calls, the carrier disconnects them, sometimes after the other side rings, sometimes before. When in this mode I have to go into modem settings and tell it to be 3G only and then I can place an outgoing call.

This leads me to believe that it could simply be a matter of having the carrier add the modem to the allow list for VoLTE. Or at least that’s the next step we are pursuing. We’ll know a lot more once we get past that point and can test outgoing VoLTE calls once the carrier allows them.


Nice! Making progress.
Thanks for the update, Kyle!

Not having read the whole upper part in detail, one question:
Which modem? Thales or Broadmobi?
I thougth first one is not available for Evergreen while the latter does not support VoLTE.
That’s why I am confused.

This is with the Broadmobi BM818-A1 modem that we ship in all North American phones. If you look up the specs for that modem you’ll see that it does claim support for VoLTE and indeed includes a toggle for it with an AT command, there just hasn’t been extensive testing of it, or adding it to allow-lists throughout global carriers yet.


@Skalman originally posted links to a Broadmobi BM818-A1 spec sheet and manual in a different thread: Librem 5 BroadMobi modem reports wrong (?) manufacturer/model info -- bug in firmware? Where to find documentation for the modem?

Specs are at: https://p.globalsources.com/IMAGES/PDT/SPEC/593/K1172549593.pdf


Kyle, thanks for providing some Purism voice on this issue, which sounds quite encouraging. To clarify, are you suggesting that enabling VoLTE on the BM818-A1 is possibly just a matter of establishing permissions for Purism to use this particular modem on a given provider network? Can you offer a short task description and timeline for getting a given modem added to a given allow list? (What is that and how long does it take?) Is Purism pursuing both T-Mobile and AT&T allow lists for the BM181-A1?

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I’m no expert in VoLTE or cellular modems, so I’m just giving my non-expert assessment based on my personal experience with trying this, along with my general expertise in troubleshooting things. Based on that, it seems the hardware does support VoLTE as it states, and works just fine for incoming calls, and that we just need to figure out why outgoing calls don’t work. It could be as simple as adding to the allow list, maybe once we do something else will come up. We’ll find out soon enough.

I really don’t want to map out a project plan, timelines, deliverables, etc. in this thread. I’m trying to participate in the forum as much as time allows, and can answer quick questions, but I can’t budget the time to research with the team and create GANNT charts, project plans, or other things like that.


We have confirmation from a member of the community that after performing the steps to enable VoLTE on their modem and rebooting a few times, they were able to make and receive VoLTE calls through their provider (1&1 in Germany).

So I’m even more confident this is just a case of getting carriers to allow it.


Thanks for looking into this! I am kinda curious how hard it is to “Get the carriers to allow it”. But sounds like we’re about to find out.

Random thought: Do carriers see this phone as just a BM818 A1, or do they see it as a librem 5 for their allowance checks? Mainly curious to know what they see and how.

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They would just see the IMEI which corresponds to the BM818 A1. Now I suppose given how few of those are out in the wild, and that it’s modem Librem 5 is known to use (web searches for the modem bring up a lot of Librem 5 pages), they could correlate the two. But they wouldn’t see it as a Librem 5 unless they decided to hard-code that correlation in their database.


Just to add, this was with the European variant of the modem obviously.


I don’t know how sceptic providers are on new modems, but I guess it is in their interest to move customers from circuit switched telephony to package switched. I think VoLTE is more efficient. VoLTE seems to be implemented differently so there may be incompatibilities between providers and calls may fallback to circuit switched calls again. Also the L5’s modems might work with some providers and not with others.

I am not an expert, but that’s what my base knowledge and Wikipedia let me believe. I am optimistic for VoLTE in Germany. :slight_smile:

pic or it never happened :stuck_out_tongue:


Has anyone tried with a modem that is certified by US carriers? I picked up an EM06-A for 35 bucks for testing once I get my librem. I realize there will most likely be other issues with a non purism modem but I wanted to try it regardless.

To make sure I understand … are we say that this particular German carrier is not picky (not checking the IMEI or modem model etc.) and VoLTE with that carrier worked without hassling the carrier? (It does of course require changes on the phone itself in order to enable VoLTE, although I assume that eventually VoLTE will be enabled out-of-the-box.)

Is it possible that the VoLTE config data in the modem is incorrect (or out of date) for the particular US carrier that you are using? (but correct for the German carrier that was tested)

I’m no expert either. So just wondering.